An incoming analog signal, for example resulting from one or more frequency transpositions of a basic signal, comprising information located in a desired frequency band (selected channel for example) and frequency components located outside the desired frequency band (channels adjacent to the selected channel), is normally converted to digital form and then subjected to specific processing operations, such as, for example, channel decoding processing operations comprising, in particular, a demodulation and source decoding processing operations.
Before performing the analog/digital conversion, the incoming signal is normally filtered so as to filter the frequency components located outside the desired frequency band (filtering residual adjacent channels, for example).
An advantageous situation would be to filter with a sophisticated filtering transfer function allowing for a minimal distortion of the signal in the desired band (selected channel) and a clear cutoff outside this band. However, for footprint and cost reasons, the analog filters conventionally used are low order and may not therefore offer a sophisticated transfer function. If a good cutoff of the adjacent channels is wanted to limit the dynamic range of the analog/digital converter, the distortion of the band (amplitude-wise and phase-shift-wise) may be greater, and the demodulation may be errored. If the integrity of the band is to be preserved, the filtering may be underdimensioned and the dynamic range at the input of the analog/digital converter may be all the greater.